#include<stdio.h>

#define PI 3.1415926 /*define constant*/
#define SQUARE(x) (x)*(x) /*define simple function*/
#define MAX(a,b) /*to do*/
#define FOR(x,a,b)  for(x=a;x<=b;x++) /*optional*/
int main()
{
	double r;
	scanf("%lf",&r);
	double area=PI*SQUARE(r);
	printf("%.5f\n",area);
	return 0;
}